He befriended 12- and 13-year-olds on social media to gain their confidence before meeting and sexually violating them

A 20-year-old man used Instagram and Facebook to befriend girls aged 12 and 13 - all from single-sex schools - before carrying out a string of sexual offences against them.

Goh Kar Aip even threatened to reveal details of one sexual relationship to the girl's school but was caught after a teacher got wind of what he was doing and a police report was made.

Yesterday, he pleaded guilty to a slew of mostly sexual offences against 10 victims.

The High Court heard that after befriending the girls via private messages, he chatted with them about sex-related topics, before progressing to asking them to send him their nude pictures. He would then meet and sexually violate them.

Goh pleaded guilty to four charges - three of sexual penetration of a minor and one of sexual assault by penetration - relating to two of the 10 victims.

Another 34 charges will be taken into consideration when he is sentenced at a later date.

These include one count of criminal intimidation for threatening to locate and tie up a 12-year-old girl when she refused his demands to send him photographs of herself. She was the only one of the 10 who did not become a sex victim.

Goh, a permanent resident, was awaiting national service enlistment in September 2014 when he started using social media to look for young girls.

He felt they were "easier to talk to" and would not look down on him for his lack of education, the court heard.

He messaged his targets privately, introducing himself as Kai. While some ignored him, others responded and chatted with him. After getting to know them, Goh moved on to sexual topics and asked them for photos of their abdomens.

Once he gained their confidence, he would ask for their nude pictures. Sometimes, he would send them pictures of his genitalia in the hope they would reciprocate.

In one case, he asked a 12-year-old to be his girlfriend on their first chat on Instagram.

GROPE

He later took her to his Hougang flat, groped her and made her commit an indecent act on him.Goh later carried out more invasive sexual acts on her at a staircase landing.

He fondled another 12-year-old, who was in her school uniform, at a staircase landing in Tampines and asked her to perform oral sex on him. He continued to sexually abuse her over the next three months.

His offences came to light when a teacher heard that a young man was harassing her students and investigated.

The teacher learnt that one of the girls in a relationship with Goh had taken three of her schoolmates to meet him.

He committed sexual offences against the girl and two of the three friends.

A police report was lodged on March 19, 2016.

A psychiatric assessment on Goh by the Institute of Mental Health found his use of physical and psychological coercion on the victims likely reflected "an underlying attitude that supports or condones sexual violence and would increase his risk of recidivism".

Goh will be back in court on March 31 for sentencing. The punishment for sexual penetration of a minor and sexual assault by penetration, is a maximum of 20 years' jail and caning.